help needed someone take a reading..

[supercharged spaniel]

can somebody do me a favour..

someone with a standard ecu...

take a reading with a multimeter on the blue temp plug on the loom (not the sensor)...with the car off, keys out...set the resistance of the meter to the ohms '20' setting and take a reading...im getting around 8.42..........please someone take a reading...thanks.
dan

[hayesey]

so you want someone to measure the resistance between the blue temp signal pin and an earth pin on the ECU loom connector?  Pins 10 and 6.

I can do this tonight when I'm at home but the reading will vary depending on temperature and my sensor will be in the air rather than water (as there's no engine in the car right now).

[supercharged spaniel]

no.. i want somone to just put one lead of the multimeter on one pin on the plug and the other on the other one on the plug...  youll need the little probe like leads rather than the clips..wether this tells me anything i have no idea all i know is with it plugged into he ecu and the car off i got 8.42 ohms.  i want to know if the resitance is higher than it should be because i tested the resistance of 3 vag sensors and got around 3 ish ohms... a non genuine one which when fitted means i have no start up mis fire had a way lower resistance of around 1.4  all three sensors had been siting in a drawer together so temperature wise were the same....i think somewhere between the plug and the ecu the resistance is too high or the ecu is faulty...i tried another ecu but whats to say that one wasnt?

[supercharged spaniel]

Im gonna try and get hold of new loom possibly...anyone swapped an engine loom before?  surely with one in place it cant be that bad?

[hayesey]

certainly could be a dodgy ECU, I had to swap an ECU because it was dodgy.  I'm not sure if that reistance reading you're taking there is meaningful, I suspect not.  Have you measured the resistance between the pins on the sensor connector and the corresponding pins on the ECU connector to test the loom?  When I had problems I went round the whole loom checking each sensor wire, haynes manual tells you which pins are what.  Worth doing before buying another loom and to be honest I'd want ot do it on the "new" loom as well as they're all just as old. 

The difference between those sensors, are you talking ohms or Kohms?  A difference of 1.5ish ohms is nothing.  They should read around 2.46Kohms at 20deg but there are pretty low tolerances so it could vary from that between different sensors.

[supercharged spaniel]

well the multimeter was set on the 20 setting im guessing its just ohms not kohms.  as for testing the corrosponding pins on the ecu side etc i really dont  know how to do that to be honest im already out my depth in electronics here...what exactly would i need to do?

[supercharged spaniel]

also...even if i did check the loom like you said..what setting should it be on...and what exactly am i looking for?  and then what?  ha ha...if a wire is faulty what do you do?  im convinced its either the loom or the ecu..its got to be...changing the sensor alters the behaviour of the problem...

[hayesey]

20 ohms or kohms though?  Those settings on a multimeter just determine the range it'll read up to in that setting, so if it's in 20ohms mode it'll read up to 20ohms and above that will just display something like "1" or "err" or some kind of out of range message.  20kohms means up to 20,000ohms.  But obviously if you are wanting to test something you expect to have a reading of something like 10ohms then putting it in 20kohms mode means it'll be to small to register.

The ECU doesn't come into the test I'm talking about, unplug it and just test the resistance between the ecu connector and the sensor connector with the sensor not plugged in.  Your just testing the wire between the connectors for breaks or dodgy connections.  The resistance should be close to zero but any wire will have a small resistance in it, set the multimeter to the lowest range setting which is probably 20ohms, if I remember correctly you may see one or one and a half ohms there.  Any larger resistances mean the loom is dodgy.  Can either strip it down and repair/replace worn out looking wires and connectors or replace it but to be honest I'd still want to test a replacement loom as it'll be just as old and used.  15+ years of use, high under bonnet temps, oil contamination, fuel contamination etc... doesn't do looms any good. 

[supercharged spaniel]

oh i know its the ecu connector sorry...ill find out about the kohms or ohms tonight.

well with the ecu disconnected by putting the multimeter probes just on the plug pins it came up with 1.  but thats not really the right way to do it...i need to do as you said....  so do i put one probe on the correct pin on the ecu connector block and one on the blue temp plug....

i did strip back the whole of the loom and checked for problems didnt find anything obvious so re wrapped the lot with new vag loom tape..looks right nice will be gutted if i chane it as ill have to do it all again...

[Fred]

Well! I happen to have my Standard ECU with me and looking in the Haynes Manual the Blue temp sensor is on pin number 10 and the Earth side can be 6 or 13.

My Loom is not with me but following the Haynes Manual this is what i`ve come up with.
Hope its Right and of Help.

You will need to have the Multimeter set on 20K (20.000 Ohm`s) or you wont get a reading.

The reading i get wichever Earth pin i used is 8.53K Ohm`s.
It may be fractionally different going from the blue temp plug on the loom to the ECU.
You may also want to check the Continuity between the Blue temp plug and the Ecu
Block connector by removing the block connector from the Ecu and Using the Diode/Audiable
setting of your multimeter.

Hope this Helps Spaniel and soz if you`ve already got that far.
Pauls guided you anyway.

Below is the Pin Layout on the Ecu.
                                               Fred.

 

[Fred]

PS, I edited the pic in Paint and theres supposed to be red lines down to the Pins with circles round them but it sems to have come out proper pooh.
The top pin on the right is pin 1 and the pin underneath that is pin 14.
You can just make out pin 10 that says Blue temp above it.
Soz for that.
               
When i was messing with my G40 trying to get it running well before we scrapped it i was up my Local
scrappy and there was a NZ Engined Polo and i took the Blue temp Sensor coz it looked brandnew.

The Guy i got the G off said he knew it was the wrong one so i put the Nz one in and to be fair it
did bugger all and it turned out that he`d been messing with the CO2 pot and stuff.
I got it running well eventually with the NZ blue one still in.

The blue temp Sensor from the G is with me here and if the code on the rim of it is the Part number then it reads 025 906 041 A.  Theres also EH2, 12V-125 max and also 43-06.
With it sat on my PC desk it measures 2.38 K Ohm.
Thats with no heating in this room and i held it with the alli bit pressed onto my palm it went down to 2.02 K Ohm.

Can someone tel me the correct part number for the blue temp sensor for the G40 please.

Fred.

[G40supercharged]

I checked the resistance between pin 10 and earth on my spare ECU and got 8.44K ohms (the 20 range on your meter must be 20K ohms). This is equivalent to measuring at the blue temp sender connector. The values we all get are the same (the slight variations in values are not significant) which suggests you have a good connection to both pins at the blue senders connector i.e your loom is OK.

I also had a look inside the ECU to see what the connections to the pin are. The way it works is that the ECU has a reference voltage of +5V which connects to earth via 2 resistors in series. The one connected to +5V is in the ECU (value is 8.25K ohms) and the one connected to earth is the blue temperature sender. The ECU measures the voltage in the middle to get a temperature reading. The resistance of the blue temperature sender goes up as it gets colder. This causes the voltage across the blue sender to increase as the temperature goes down.

Crappy attempt at a diagram below:

+5V
I
8.25K resistor
I
------>  to ECU voltage measurement
I
blue sender
I
earth

Voltage at ECU pin 10 is 5 x blue sender resistance/(blue sender resistance + 8250)

Here is a table of typical Digifant temp sender resistances for different temperatures from the Haynes engine management manual. (These are typical for Digifant rather than G40 specific but the voltages Haynes suggest fit correctly with the 8.25K resistor I found in the ECU.)

Temp       resistance
0             5K to 6.5K
10           3.2K to 4.2K
20           2.1K to 2.9K
40           1.0K to 1.4K
60           520 to 670 ohms
80           280 to 370 ohms

This gives a temperature of around 20 degrees for all of the genuine senders that were checked which sounds OK. The non genuine one you tried that made it run better (lower resistance) would have indicated a hotter engine to the ECU. 

To check your ECU is outputting the correct reference voltage put the meter on DC voltage measurement (20V range). Start car then disconnect blue temperature sender and measure voltage across the connector pins. This should be 5.0V.  (Start with sender connected or ECU will see it as a fault. Don't measure resistance with the car on as the meter puts out a voltage itself for this type of measurement and you may cause damage). This check will also verify you have a good connection through the loom. 

Nick

[supercharged spaniel]

really appreciate the help lads i really do..

anyways just to re cap..im really numb with electronics but ill explain what ive done...

started the car from cold...mutlimeter set on DC with 20v selected, disconnected blue temp sender and tested the pins on the plug and got 4.93v  which is lower than the 5.0 v you recommended Nick.  does this suggest a problem with the ecu?  or is its value insignificant?

testing 2 vag blue senders in my hand now which have been together (ahh) in my drawer so room temperature with ohms set on 20k i get 2.30 plus or minus a couple  so this would suggest that the senders im using are fine.

testing the resistance with the car off on the blue plug on the same setting i used to test the senders above i got around the same you and fred got, around 8.47 i think it was so this suggests an ok loom doesnt it? 

please tell me im going somewhere with this?  my hope is that the lower voltage is significant enough to warrant a duff ecu and therefore the problem could possibly be coming to some close?  otherwise where from now?


and finally...Fred..all blue senders for mk3's are the same the part numbers of the two in front of me now are  as yours..025 906 041 A

thanks again...dan

[Fred]

Nice one Nick.
I kinda new someone would clarify things better.
Its fair that i have some electronics knowledge from the Amateur Radio course i did
some years ago but this engine management/ECU stuff is all new to me.
From your chart i`ve just measured the blue temp sensor to be 3.16K Ohm`s so
making the temp in my room around 10 degrees.
Warming it again in my hand dropped it to 2.17K Ohm`s so around 20 degrees.
Glad that i was correct for the distance i got with it.

And to Dan,
Thanks for the temp sensor part number.
This means that both i have are correct and functioning correctly.

Below is a pic of my multimeter set on the 20k setting and 3 clicks to the left on
the main dial is the continuity/diode test setting.
As Nick says- On the continuity/diode test setting the multimeter puts out a voltage
and can damage certain sensitive electronics and therefore if you want to check for
brakes in wiring looms then be sure to disconnect the loom at both ends and put a
probe at each end of the wire to be tested.
My meter give an audiable beep on this setting.

[G40supercharged]

The value of 4.93V sounds like it's all working correctly (the difference from +5.0V isn't significant; the voltage variation due to using different senders is much greater than this). 

The fact it worked better with a non genuine sender indicating a higher temperature suggests your engine doesn't like working under the ECU's 'cold start' conditions. Could be too much fuel going in or the base timing is out. If I remember correctly you were also having alternator issues; it could be the battery that is a bit tired as I've had this cause odd electrical problems.

Nick